My '87 Spider has a whirring noise coming out of the back end. It's directly related to vehicle speed, not engine revs or anything else. It becomes noticeable around 45 mph and by 65 is kinda loud. I recorded it today on the highway, but just discovered it won't upload to this forum. So imagine a high-pitched "whuh whuh whuh whuh whuh" sound that gets faster and higher in pitch and volume with speed. I'm thinking it's a rear wheel bearing but wanted to get any/all ideas before pulling the rear axle apart. Thoughts?